Thursday, August 09, 2012

Will the Warmer Lake Increase Lake Effect Snow in November?

I recently posted on Facebook and Twitter the Lake Erie water temperature reaching 80 for the first time since 2001. This prompted emails and comments asking whether or not the warmer lake temperature will have an impact on lake effect snow. Here are several points to keep in mind before we take a look at the factors that effect the temperature of the lake:

* The difference between most summers Lake Erie water temperature to this summer's record temperature is fairly small. In 2010, a very warm summer which got an early start in April, the lake water temperature reached 76 for several weeks. In 2009, a much cooler summer, the water temp reach 74 for a few days in mid August. While these summers were markedly different, the lake water temperature difference was only a few degrees.

* The official water temperature is taken at the Cleveland Crib (water intake several miles offshore) and at a depth of 40 feet. So the surface temperature may be several degrees warmer than the official reading

What are the factors that have contributed to the lake water temperature trend this summer?

1. Timing

The timing of this summer's first burst of heat was a bit different than in years past. The 11 days stretch in late June into early July was the warmest and longest stretch in late June/early July since 1949. That stretch was only 9 days. This sudden surge of heat occurred at just the right time of early summer when the lake was the most vulnerable to rapid warming.

The Lake Erie water temp averages a rise of 5 degrees from June 30th to July 15th--67 to 72. By the end of July, the water temp was near 80! As of August 9th, the water temp is still at 80.2. No significant storms

Lack of any strong storm systems over the lake kept the lake still. A strong front produces strong wind shifts horizontally. As storms develop, cold downdrafts race out of those storms. These motions "stir" the lake mixing the warmer water on the surface with the cooler water beneath resulting in a cooler lake.

3. Little snow melt in late winter/early spring

Spring snow melt would have resulted in more runoff into the lake from the tributaries like the Cuyahoga, Chagrin, Grand and others overturning the surface water keeping temperatures cooler longer.

Check out the sediment from the runoff last March in this high resolution satellite photo

Compare this with an early August high resolution satellite shot. Notice very little sediment from runoff

4. Old Fashioned Heat

Continuous daytime temperatures in early July above 90 with overnight lows above normal aided in the warming. We've had 23 days so far.

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Which leading us to The Big Question: Will water temperatures at 80 (higher in isolated spots) play a role in increasing lake effect snow in early winter?

The first thing to remember is the actual water temperature isn't the key component to lake effect snow. Its the DIFFERENCE between the lake temperature AND the temperature of the colder air moving over the water.

In most years, the water temperature begins to drop at roughly the same rate in September and October regardless of the highest water temperature reached during the summer. The graphic below compares the cooling of Lake Erie in the fall of three years. 2010--a very warm summer--to 2009, a relatively cool summer followed by 2001 which was the last time the lake reached 80.

Does the peak temperature and its duration impact the temperature drop? Not at all. The drop each year was the same even with prolonged time at the highest temperature

By the time lake effect snow season begins, the water temperature year-to-year is roughly the same. So unless we get an early season shot of cold air, early season (late October-early December) lake effect snow shouldn't be effected by the somewhat warmer Lake Erie water.